This invention relates to a membrane process for drying liquid hydrocarbons to low levels of water.
Hydrocarbons are commonly used as motor fuels and as chemical feedstocks in polymerization and other reaction processes. Hydrocarbons may absorb moisture during shipping, storage, and use. The presence of water in hydrocarbons is generally undesirable because of the possibility of corrosion of piping and equipment. An additional problem that may be encountered is the freezing of piping and equipment in cold weather. Further, the presence of water in motor fuels may cause poor engine or motor performance. Water contamination may also interfere with the hydrocarbon's intended use as a chemical intermediary during polymerization. For these and like reasons, it is frequently desirable to remove water from hydrocarbons to low levels.
Removing water from hydrocarbons to low levels can be costly and complex. Conventional methods of removing water include mechanical separation such as decanting. However, mechanical separation only removes water which exists as a separate phase and does not remove water which is entrained or dissolved in the hydrocarbon phase. Mechanical separation is insufficient when water must be removed to low levels. Distillation has also been used to remove water from hydrocarbons, but distillation is an energy-intensive process. Further problems associated with distillation include limitations on the level of water which can be removed because water forms azeotropes with many hydrocarbons. Other methods of removing water which have been used include the use of drying agents such as glycols, silica gels, and molecular sieves. Such systems are generally large and expensive. Problems with these drying methods include a limited absorption capacity for water, which requires replacement or regeneration of the drying agent. Such drying processes are therefore batch rather than continuous. If continuous operation is required, additional capital must be expended to install duplicate drying columns or beds which can be used when the completely exhausted columns or beds are being regenerated or replaced. Effluent from the columns or beds generally must be monitored to determine when the capacity for water absorption has been reached in order to determine when regeneration or replacement of the drying agents is required.
What is needed is a continuous, unattended, and inexpensive process which will dry liquid hydrocarbons to low levels of water.